Chromatographic sampling system



Dec.

Filed Aug. 22, 1957 H. N. CLAUDY CHROMATOGRAPHIC SAMPLING SYSTEM 4Sheets-Sheet 1 INVENTOR. H. N. CLAUDY A7' RNE 5 Dec. 25, 1962 H. N.cLAuDY 3,069,894

CHROMATOGRAPHIC SAMPLING SYSTEM Filed Aug. 22, 1957 4 Sheets-Sheet 2A771 Ney H. N. cLAuDY 3,069,894 cHRoMAToGRAPHIc SAMPLING SYSTEM 4Sheets-Sheet 3 EN@ xm@ mw uw@ Dec. 25, 1962 Filed Aug. 22. 1957 um@ Mum@ am@ 7g INVENTOR. H. N. CLAUDY A 7' RNE 3,069,894 Patented Dec. 25,1962 rthis invention relates to a sampling system.

ln various types of analytical instruments, particularly chromatographicanalyzers, numerous samples are analyzed in succession by passing them.through a chromatographic column with a carrier gas, such as helium. lInsuch instruments, it is desirable that a definite volumetric amount ofthe sample be trapped in a loop or conduit and then the trapped sampleof delinite volume is forced into the column by the carrier gas. Withsuch a system, a valve is provided which, in one position, passes thecarrier gas directly to the column, and passes the sample gas throughthe loop to a vent, thus trapping the sample in the loop. in anotherposition or `the valve, the sample flows directly to the vent line,while the carrier gas passes through the loop into the chromatographiccolumn, thus sweeping the trapped sample into the column. Where smallvariations occur, due to the geometry of the Valve, one port therein maybe operated slightly before or after another port, thus resulting invariations in pressure and, hence, in amount or" the sample trappedWithin the loop. This may result in serious inaccuracies in thesubsequent analysis.

ln accordance with the present invention, such pressure variations areeliminated by cutting oft the flow of sample to the valve just beforethe end of the period during which the sample flows through the loop tothe vent pipe. As a result, the pressure within the loop falls to aconstant regulated value before the valve is actuated to the position`vhere the carrier gas liows through the loop pushing the sample intothe column. Due to the resulting pressure equalization betweensuccessive samples, the same amount of sample is obtained in each of thesuccessive analysis periods, thus obviating inaccuracies resulting fromsuch variations in sample quantity.

Another important advantage of the present invention resides in flushingout the sample valve housing with helium, thus preventing a combustiblemixture from forming, should leakage ot the sample occur at lthe valveports.

it is an object of the invention to provide `a novel pressureequalization system.

it is a further object to provide `a system to prevent presence or acombustible mixture in a valve housing.

it is a still further object to provide a system which is simple inconstruction, reliable in operation, and contributes importantly to theaccuracy of analysis in an analytical instrument such as a gaschromatographic anali zer.

Various other objects, advantages and features of the invention willbecome apparent from the following detailed description taken inconjunction with the accompartying drawings in which:

FIGURE l is a schematic tlow diagram of the chromatographic analyzer ofthe invention;

FlGURE 2 is a vertical, sectional View, partly in elevation, of thechromatographic column assembly;

FlGURE 3 is a perspective view of the sample valve with the parts indisassembled relation;

FIGURE 4 is a vertical, sectional View, partly in elevation, of thesample valve;

FGURE 5 is a schematic circuit diagram of the timing and programmingsystem;

EiGURE 6 is a perspective View of the timing mechanism;

FIGURE 7 is a detail view of the timing disc and tab;

`FIGURE 8 is a View of a chart in bar graph form; and

FIGURE 9 is a view of a chromatogram With a modi- Ylied programmingsystem.

Referring now to the drawings in detail, and paiticularly to FIGURE 1,the sample to be analyzed is fed into the instrument by a conduit 10which leads through a liow meter 11 to a three-Way solenoid valve 12. lfthe sample is liquid, it is vaporized in a unit 10a under xed conditionsof temperature and pressure. This increases its volume per unit Weight,thus simplifying volume measurement. lf the vaporization temperature ishigh, all parts of the system have to lbe at a high temperature to avoidcondensation. This is avoided in the present apparatus by operating thesystem at reduced pressure, such that the partial pressure of thehighest boiling component present is not exceeded. This can beaccomplished by a vacuum pump and a pressure recorder controller llib,FIGURE 3. In one position, the valve 12, FIGURE l, discharges the samplethrough a line 13 and a llame trap 1li to a flare pipe 1S. With thevalve in its other position, the sample passes through a line 16 to arotary valve 18 controlled by a motor, not shown, at the end of a shaft1de.

From the valve 18, the sample may be directed into a sample loop 2d or,alternatively, it may be discharged through line 21, and line 26a andthe llame arrester 14 to the vent 15.

A supply of carrier gas, such yas helium, is introduced to the.instrument by a line 22, this gas passing through a liow meter 23a, andone cell of a thermal conductivity measuring assembly 17 to the valve1S. From the valve 18, the gas may be passed through the loop 20 to aline 23 which leads to a chromatographic column 24, the material leavingthe column passing through a line 25 and another thermal conductivitycell of the assembly 17 to a vent conduit 25a communicating with theline 20a.

1t will be noted that the inlet lines 16 and 22 pass through a preheatercoil 26 so that they are at the same temperature when they pass throughthe column and thermal conductivity cell assembly. As will behereinafter explained in greater detail, the parts. 17, 18, 24 and 26are mounted within a thermally shielded cover 27 which is accuratelymaintained at a constant temperature.

in operation, valve 18 is first actuated to pass sample material throughthe loop 2li to the vent. pipe While the helium gas passes through thecolumn 24. Thereafter, the solenoid valve 12 is actuated to close olithe line 16 and pass the sample to the vent pipe 13. As a resul-t, aportion of the sample to be analyzed is trapped Within the loop Z@ atatmospheric pressure. The valve 18 is then actuated to pass the heliumgas through the loop 2li and, thence, into the column 24, therebypushing the sample material ahead of it through the column. In thismanner, a deiinite predetermined amount of sample material is passedthrough the column at each operation, the effect of pressure variationsbeing eliminated by the described operation of the solenoid valve 12.This provides precise volume reproducibility ofthe sample.

The helium carrier gas entering the column passes through one cell ofthe thermal conductivity assembly 17 While the carrier and sampleleaving the column pass through the other cell of this assembly. As aresult, as the separated components of the sample are eluted from thecolumn 24 in succession, the resulting conductivity changes in thesample cell produce an unbalance Voltage in a bridge circuit to behereinafter described. This voltage varies in accordance with the natureand amount of each dilerent component in the sample and thus permits itto be analyzed as to its composition. It will be understood that lightermaterials, such as methane, ethane and the like, will be the first toleave the chromatographic column 24 and thereafter the heaviercomponents will leave the column, there being a definite break or changein thermal conductivity as the nature of the component leaving thecolumn changes. This enables the composition of the sample to beaccurately determined by measuring the difference in thermalconductivity between (a) pure helium, and (b) helium plus the componentbeing analyzed.

Referring now to FIGURE 2, it will be noted that the cover 27 includesan outer metal shell 27a, and an inner metal shell 27h, the spacebetween these shells being filled with a suitable insulating material27C, such as fiber glass. A heater 27d is wound exteriorly of the shell27h, and this heater is thermostatically controlled by a mercurythermostat 27z and a conventional thyratron circuit, not shown, tomaintain a constant predetermined temperature within the unit. Theassembly is provided with a cover, consisting of an outer plate 27e, aninner plate 27j, and a layer 27g of insulating material, such as liberglass, between these plates.

Attached to the plate 27j, and mounted interiorly of the shell is thepreheater assembly 26 which includes an annular support 26a having coils26h wound around it which form a part of the respective lines 16 and 22,FIGURE l.

Mounted concentrically with respect to the assembly 26 is thechromatographic column assembly 24 which includes a coil 24a filled withabsorptive material, such as activated charcoal, silica gel, crushedrebrick impregnated with .a silicone oil or dimethyl sulfolane,molecular sieve material, or the like, this coil being wound interiorlyof an annular member 24b.

The cell assembly 17, valve assembly 18, and related parts are mountedaxially of the coils 24a and 26h, the valve having an outwardlyprotruding shaft 1&1 which is secured by a coupling 18b to an electricmotor 30 having an annular mounting piece 30a. The motor is thus mountedoutside the housing 27.

Also attached to the shaft 18a is a cam 31 which actuates a microswitch32 connected to the motor Sti to the end that the valve is rotated .apredetermined distance each time current is supplied to the motor.

It will be evident that the housing thus provided for the thermalconductivity cells, valve assembly and chromatographic column ismaintained accurately at a predetermined temperature while the analysisis being carried out. Also, by virtue of the preheater coil 2lb, thesample and displacement gas streams are effectively brought to theinterior temperature of the housing before they enter the analysis coil.Excellent heat transfer is obtained between the parts due to mounting ofthe valve 18 next to the assembly 17 with resultant elimination ofseveral conduits which would otherwise be required. Finally, a verycompact and rugged structure is provided which is capable ofwithstanding hard usage.

The structure of the valve assembly 18 is shown in more detail byFIGURES 3 and 4. It will be noted that the valve has a base 18C which issecured to the cell assembly 17. A plurality of ports are included inavalve ring 18d, and these ports are interconnected by grooves 18e formedin a back-up ring 181. The ring 18f can be rotated by the shaft 18a. Itis connected thereto by a spring 18g and a spring follower-couplermember 18h. Also cooperating with the shaft 18a are a thrust bearing181', a bushing 18]', a packing 18k and a packing nut 18m. It will benoted that the shaft carries the cam 31 and microswitch 32 described inconnection with FIGURE 2.

The ring 181 has two positions relative to the valve seat 18d, and theports in the valve seat 18d are connected, respectively, to the ventline 21, the sample supply line 16, one end of the sample loop 2t), theinlet line 23 to the chromatographic column 24, the helium inlet line22, and the other end of the sample loop 2t?.

In the rst position, the slots 18e are so disposed as to connect thesample line 16 to the vent line 21 through the loop 20, while the columninlet is connected to the helium inlet line 22. As a result, the samplematerial flows through the loop 20 While helium or other carrier gasflows through the chromatographic column.

In the second rotary position of the ring 18e, displaced 60 from thefirst position, the slots 18e are so disposed that helium gas passesthrough the line 22, the sample loop 20, and the line 23 to the column24 while the sample supply line is connected to the vent pipe 21.Accordingly, the sample is vented, while the helium gas displaces thesample trapped in the loop 2@ and forces it to the column 24 where it isanalyzed in the manner previously described.

As previously indicated, the solenoid valve 12, FIG- URE l, closes ashort time before the sampling valve 13 is moved to its second position,with the result that the sample pressure drops to atmospheric pressurebefore the sample trapped in the loop is fed to the chromatographiccolumn. This prevents variations in pressure and, hence, in the amountof sample flowing to the column during each cycle of operation. As willhereafter become apparent, this valve is actuated automatically as theanalyses are carried out.

It is a feature of the invention that the gas leaving the column 24 isutilized as a purge gas for the housing 182 of valve 18. Thus, this gaspasses from the column outlet 24x to the interior of the housing 181 ofvalve 13 by way of bore 18W, and leaves the housing through a bore 15x,see FIGURE 4. Since this gas is essentially inert, a combustible mixturecannot form in the housing of valve 18 should leakage at the valve portsoccur.

In FIGURE 5, there is shown a detailed electrical circuit of aprogrammer which separates portions of a recording into differentsections corresponding to the various components of the sample as theyissue from the outlet of the chromatographic column 24. This programmingcircuit adjusts the sensitivity of the recorder circuit for eachindividual component, and may be adjusted to provide a bar graph type ofrecorder output. The circuit is desirably mounted in an air-purgedcontrol box. All open switch contacts are mounted in an explosion-proofbell attached to this air-purged control box, and all switches in thecontrol box are mercury switches.

To this end, two thermal conductivity cells 17a and 17h, forming a partof the assembly 17, are connected in a Wheatstone bridge circuit withfixed resistances 35, 36 `and a potentiometer 37, the contactor of whichis connected to a positive power supply terminal 38. It will be recalledthat one of these cells is exposed to the incoming helium gas while theother cell is exposed to the eiuent from the column 24, FIGURE l. Thus,the bridge produces an output voltage across conductors 39 and 4t?,FIGURE 5, representative of the difference in thermal conductivitybetween (a) helium and (b) helium plus the particular component passingout of the column. The output voltage of the bridge is varied beforebeing `applied to the input terminals 39a, 3919 of a suitable recorderfor two reasons. First, it is desired to adjust the outputs to a desiredpercentage for full scale recorder reading, and second an adjustment isnecessary to compensate for peak height differences for severalcomponents of the same percentage since the concentration of a componentis proportional to the area under the peak shown by the recorder forVthat particular component, and the peaks are not all the same Widthsfor various components.

To this end, a selector switch 41 is provided having four banks 41a to41d of contacts, a stepping coil 41e, a set of interrupter contacts 411and a set of off-normal contacts 41g. A series 42a to 42e ofpotentiometers have their xed terminals connected to the conductor 39and to the respective contacts of the switch bank 4111. The contactorsof these potentiometers are connected, respectively, to the terminals ofswitch bank 41C.

Normally, one potentiometer 42 is provided for each componen-t of thesample stream which is to be analyzed. The selector switch operates, ashereafter described, to switch the appropriate one of the potentiometersinto the ycircuit as the sample mixture is resolved into itscornponents. ln th-is manner, the potentiometers can be set duringcalibration with a sample generally similar to the ones to be analyzedto present a preselected percentage of a component as full scale on therecorder. Then, the recorder will not go oifscale during analysis, butan adequate height is obtained for the recording peak of each componentof the sample under analysis.

A bank 43a to 43e of indicator lamps is provided to show which componentor the sample is being analyzed. One terminal of each lamp is connectedto a lead 43] which extends through a switch to an A.C. supply terminal43g while the other terminals of the lamps are connected to therespective contacts of the switch bank 41a, the movable contact or"which is returned to the other side of the line.

The operation of the programming circuit is controlled by a disc timingdevice or" novel construction and operation. Referring to FGURES 5, 6and 7, this unit, which is generally indicated by reference numeral 44,includes a timing disc 44a xed to a shaft adb of a motor 44C. The motor,in turn, is connected by a switch to supply terminals ddd, FGURE 5.

Complementary slots 44e and 4f are formed in opposite faces of the discadjacent the edge thereof. Any desired number of tabs 44g can be mountedat desired locations along the edge of the disc. Each of these has anoutwardly protruding tab portion Alli/t, FIGURE 7," `formed integrallywith a pair of spring lingers 441'. These iingers fit into the slots44e, lief and hold the tabs in desired position at the edge of the disc.The disc further has one or more openings 44]' formed therein near itsedge.

The tabs 44g are arranged to interrupt a beam of light passing from alamp 45a to a photoelectric cell 45h. The opening 44j is arranged topass a beam of light from a lamp 55C to a photoelectric cell 45d whenthe disc reaches a predetermined angular position. The lamps 45a, 425eare connected in series with the secondary Winding of a transformer 45e,FIGURE 5, the primary winding of which is connected to the voltagesource 44d.

ln operation, it will be evident that the tabs 44g interrupt the beam oflight passing to the cell Sb any desired number of times during eachrevolution of the disc, and at any desired angular positions of thedisc. Moreover, the number of interruptions and their angular positionscan be readily varied merely by removing tabs from the disc and placingother tabs thereon at the desired angular positions. The openings 44jprovide a pulse of light to the cell 45d at any desired angular positionof the disc, for example, for reset purposes.

The tabs Atag may thus be regarded as pulse-producing devices whichinterrupt light from the source 45a to the sensing dev-ice 45h. lt willbe evident that this provides a Very ilexible timing mechanism havingobvious utility where pulses of variable timing and width are to beproduced in a cyclic manner. in the present system, the tabs are used toprovide a predetermined length for the analysis period of each componentof the sample, the less volatile components of the sample, of course,requiring more time to pass through the chromatographic column than themore volatile components. As Will become evident later, .the opening 44jprovides an index pulse which repeats the sequence of analysisoperations.

This disc timing system is highly advantageous in that it providesimproved resolution, accuracy and flexibility compared to cam timers, inaddition to eliminating the problems of cam wear.

The photoelectric cells ib and La? control the irnpulsing circuits ofthe selector switch 41. To this end, one terminal of the cell 45d isgrounded, the other terminal being connected through the operatingWinding of a relay r6 and a fixed resistance 47 to a positive supplyterminal 4S. The relay i6 has a set of normally open contacts which areconnected in circuit with a positive supply terminal i9 and all contactsexcept the first of a reset bank Alla' of the selector switch. Thisreset bank is further connected to ground through the operating windingof a rel-ay 5d, and through the off-normal contacts lig to a terminal 5lconnected to the arm or the switch bank lila'. The wiper connected toterminal Si wipes by the bank Contact also attached to the terminal l.This is also true of the wipers of the other banks of the selectorswitch and the bank contacts connected thereto.

One terminal of the photoelectric cell 15b is connected to ground, andthe other terminal is connected through the operating winding of a relay52 and a fixed resistance 53 to a positive supply terminal Se. TherelagI S2 has an arm 52a which is connected to ground through acondenser 55. This arm coacts with a normally open `contact which isconnected by a fined resistance 56 to a positive supply terminal S7, andthe arm further coacts with a normally closed contact having a lead eltlsecured thereto, which lead is connected to ground through the step-pingcoil file of the selector switch. The latter coil is connected inparallel with a unit including a fixed resistance 59 in series with acondenser dit. The lead 5S is further connected to ground through theoperating `winding of a relay 6l and to the termina-l Sl through theinterrupter contacts tlf of the selector switch and a normally opencontact set of the relay Sil.

ln operation, the photoelectric cell lh is energized at all times when atab is not positioned between it and the lamp 45a. Accordingly, therelay 52 is energized and condenser S5' is charged. When a tab idgpasses between the source and the cell 45h, a pulse of cun rent passesfrom the condenser 55' to the coil elle, thus causing the switch toadvance one step. For a purpose to be explained later, the relay el isalso momentarily energized by each such pulse. Thus, each tab causes theswitch to be advanced one step causing a new potentiometer i2 to beinserted in circuit with the cells l7n, ll'b and a new indicator lamp i3to be energized. The timed periods thus provided correspond with thetimes required to analyze for various components of the sarnple passing-to the chromatographic column.

The photoelectric cell 45d is normally de-energized, but providescurrent when the opening 44j passes between the lamp il-5c and the cell45d. When this occurs, power is applied to the reset bank tid and relaySil is energized. This causes current to ilow to the terminal 5l and,thence, to the stepping coil die through the contacts tlf and thenormally open contacts of relay 5@ until the switch reaches its normalposition in engagement with the first bank contact. The oft-normalcontacts dlg close only as the Wiper goes by its own terminal. Other-Wise the wiper would home on its own connecting termina] instead of theiirst bank contact. As will be eX- plained later, when the selectorswitch is reset in the manner just described, a new series of analyticaloperations is initiated.

Each time a new cycle of operation is initiated by the describedenergization of the photoelectric cell 45d, the relay Si? is energized,thus supplying current through a normally open contact set to a motor62a from a supply terminal 62b. These are elements of a timer 6.2 whichhas a cam 62C controlling a holding circuit to the motor from a supplyterminal 62d to the end that the timer motor operates through a completerevolution despite opening of the contacts of relay 541i.

The timer further includes a cam 62e which supplies current from aterminal 62f twice during each cycle of the timer 62 to the motor Sil,FIGURES 2 and 5. When thus energized, the motor effects a 60 revolutionof the valve 18 and rotates the cam 3l xed to the shaft 18a.

The initial movement of this cam completes a holding circuit from asupply terminal 62g through normally open contacts of the microswitch 32and the normally closed contacts actuated by the cam 62e.

A condenser V62h is charged from the terminal 62g by a rectifier 62.5and a tixed resistance 62j. When the valve motor completes its 60revolution, the microswitch 32 is actuated to interrupt the motorholding circuit. At the same time, condenser 62h discharges through thenormally closed contacts of the microswitch 32 and the normally closedcontacts actuated by the cam 62e. This discharge of the condenserabmptly stops the motor and prevents overtravelling of the valve.

A cam 62k forming a part of the timer actuates the solenoid valve l2,FIGURES yl and 5, from a terminal so that this solenoid valve closes ontthe ow of sample a short time before the valve 13 is actuated to passsample from the loop Ztl into the chromatographic column 24. In somecases, this valve may be operated pneumatically rather thanelectrically, as shown.

It will be apparent, therefore, that the timer 62 actuates the valve 13in the manner previously explained in timed relation to the operation ofthe solenoid valve l2.

It is a feature of the invention that the present programming circuit isadapted to produce a bar graph display upon the recorder chart, asillustrated by FIGURE 8. To this end, a cam 62n forming a part of thetimer `62 supplies current, when actuated, to a terminal 64. This, inturn, energizes a timer motor 65a which closes a set of contacts 65hconnecting the terminal 64 to a supply point 65C. At each actuation, thetimer 65 supplies current to the terminal `64 for a timed period.

The terminal is further connected to the winding of a relay 66 havingcontacts 66a which short-circuit the recorder input terminals Sn, 3%when the relay is actuated. When the relay is cle-energized, therecorder input terminals are connected through the potentiometers 42 andbank contacts @lb and tlc to the thermal conductivity bridge.

The terminal 64E is further connected through a normally open contactset of a relay 6l and through a normally closed contact set of a relay67 to a supply terminal 63. Finally, the terminal `64 is connectedthrough a normally closed contact set of the relay 67 to a chart motor69".

When the terminal 64 is supplied with current by the cam 62:1, therecorder terminals are shortcircuited and the chart motor 69 is drivenfor a length of time determined by the length of the rise of the cam62u. Also, when the contacts of cam 6211 are open, the recorder contactsare short-circuited and the chart motor driven for a shorter period oftime, determined by the setting of the timer 65. This occurs each timethe relay 6l. is energized along with the stepping coil die throughde-energization of the relay 52 by passage of a tab 44g between the lamp45a and photoelectric cell 45h.

When the relay 67 is energized manually by operation of a switch 67a,the chart motor is driven in the con- Ventional manner directly from thevoltage source 68.

n the over-all operation of the system, a sample having approximatelythe same components as the one to be analyzed is manually passed throughthe system, and the times required for each component to be successivelyeluted from the chromatographic column are determined. This enables thetabs to be set upon the disc timer, FIG- URE 6, to provide the requiredintervals for the analysis of the respective components of the sample.The potentiometers i2 are set to give the desired full scale percentagesfor the respective components to be analyzed. The analyzer is then readyfor operation, when a sample to be analyzed and helium gas are suppliedto the equipment.

Assuming that a bar graph display, FIGURE 8, is desired, the relay 67 isde-energized, and rotation of the 8 timer disc `lieta is initiated bymanipulation of the switch connected to terminals 44d, FIGURE 5.

With the operation thus initiated, the opening 44j passes between thelamp `iSc and photoelectric cell 45d. This supplies power to the resetbank of the switch 41 causing it to return to its rst position. At thesame time, the timer 62. is energized.

During the first part of the cycle of timer 62, the sample valve 1S,FIGURE l, is so positioned that sample material traverses the loop 20and the helium carrier gas is fed through the column 24. During thisinterval, the chart motor 69 is running and the recorder input terminalsare short-circuited through supply of power to the terminal 64 from thecontacts of the cam 6211. This produces the initial straight portion ofthe bar graph display denoted by reference numeral 7d, FEGURE 8.

After a period sufliciently long to allow the loop 20, FIGURE 1, tobecome lled with the new sample, the solenoid valve 12 is actauted bythe cam 62k, FIGURE 5, to stop the flow of sample through the line 16and pass the sample to vent pipe 13. This allows the pressure within theloop to drop to atmospheric pressure for constant volume metering.

Thereupon, cam 62u opens the contacts associated therewith, thusinterrupting the flow of current to the chart motor `69. The timer acontinues to run as long as the contacts of the cam 6211 are closed. Thetimer 65a will make 5 revolutions while the contacts of cam 62m areactuated. Both may release at the same time. It is preferable to havethese contacts open slightly before the timer 65a has completed its 5thcycle. The effect of rotation of timer 65a will not show up on therecorder since the cam contacts 62 control the recorder during thisinterval.

The cam 62e next initiates a 60 rotation of the motor Sti, thus causingthe inlet valve lil, FIGURES l and 5, to move to a position where thesample is passed to the vent pipe, and the helium carrier gas is passedto the chromatographic cell 24 through the sample loop Ztl, thus pushingahead of it the volume of sample trapped in the loop.

The most volatile component of the gas rst issues from the column andpasses through the thermal conductivity cell bridge 17. Thepotentiometer 42a has been previously adjusted to give a proper spreadon the chart, based upon prior knowledge of the approximate compositionof the sample. Recalling that the chart motor is stopped, it is evidentthat the pen of the recorder will trace a vertical line 71, FIGURE v8,upon the chart, the height of this line being representative of theconcentration of the most volatile component of the sample.

At the end of the period allotted for analysis of the rst component, atab 44g, FIGURES 5 and 6, on the disc 44 interrupts the beam of lightpassing from the lamp 45a to the photoelectric cell 45h. The resultingdeactuation of the relay 52 sends a pulse of current through thestepping coil 41e, FIGURE 5, of the selector switch and also closes therelay `6l. The described energization of the stepping switch connectsthe potentiometer 4217 in circuit with the thermal conductivity bridgeand the recorder input terminals so that the proper recorder range isselected for the second most volatile component. Also, the pilot light43h is energized signifying that analysis of the second component istaking place.

The described energization of the relay 61 energizes the timer 65 andcauses the chart motor to run for a relatively short timed period. Also,relay 66 is energized to short-circuit the recorder input terminals. Asa result a second horizontal line 72 is formed upon the recorder chart.Preferably and advantageously, the period represented by line 72, forexample, 6 seconds, is substantially shorter than the period representedby the line 70, for example, 30` seconds.

At the end of the cycle of the timer 65a, the contacts 65h are opened,thus de-energizing the chart motor. Also, the relay 66 is de-energized,thus connecting the recorder input terminals to the potentiometer andbridge circuit. The recorder pen then again traces a vertical line, theheight of which represents the concentration of the second most volatilecomponent of the sample. The potentiometer 4t2-ib has been previouslyadjusted to give an appreciable span for this component on the recorderchart.

This sequence of operation is repeated for each component of interest inthe sample, the selector switch being successively actuated to place theproper potentiometer in the bridge circuit, light the appropriateindicator lamp 43, and disable the recorder input while the motorproduces a short horizontal line 72 on the graph. Thus, the results ofthe analysis are presented in convenient bar graph form for readyinterpretation.

it will be understood that the length of the total cycle can be variedby changing the speed of the motor 44C, FIGURES 5 and 6.

When the last component has been analyzed, the opening 44j, FIGURES land 5, passes between the lamp 45e and photoelectric cell 45d. Thisresets the selector switch and again actuates the timer 62 to provide arelatively long line 7@ between successive cycles. Thus, the lines onthe chart are separated into easily readable groups, each representingone cycle of operation of the instrument, each group containing severallines representing the concentration of the respective components of thesample.

The instrument is also flexible in that the conventional form of graphicrepresentation can be readily obtained. This is done by actuating theswitch 67a, FGURE 5, to energize the relay 67. Thereupon, current isapplied continuously to the chart motor producing a record such as isshown by FIGURE 9 with peaks 75, 76 and 77 representing theconcentrations of the different components in the sample. Of course, theproper potentiometer i2 is inserted for each component analyzed so thatthe proper spread upon the recorder chart is obtained.

Certain of the selector switch positions may be used, if desired, forautomatic recorder zero, detector balance, and automatic recorderstandardization wherein the quantity to be balanced or standardized iscompared with a control value, and the difference utilized to vary animpedance so as to maintan the balanced or zero condition.

It will be apparent that the objects of the invention have been achievedin providing a chromatographic instrument which is of rigid constructionand well adapted for use in hazardous locations. The output is presentedin a form which can be readily analyzed, and the programming `isautomatically controlled so that the proper chart spread is obtained foreach component. Also, the timing disc with the removable tabs permitsthe same instrument to be readily adjusted for analysis of samplestreams of widely-varying composition. .'Finally, the sampling system,by allowing pressure to drop to atmospheric in the sample loop beforethe analysis cycle, prevents error which might result through pressurevariations from one cycle to the next.

I claim:

l. A sampling system comprising, in combination, a sampling valve havingsix ports formed therein and comprising a fixed element and a movableelement, sample inlet line connected to the first port of said valve, acarrier gas inlet line connected to the second port of said valve, avent conduit connected to the third port of said valve, an outletconduit connected to the fourth port of said valve, and a conduit orloop connected between the iifth and sixth ports of said valve, timingmeans cyclically operable to move said movable element to a firstposition during one portion of each cycle 4and to move said movableelement to a second position during another portion of each cycle, saidmovable element in the iirst position connecting said rst port to saidfifth port, ysaid sixth pont to said third port and said second port tosaid fourth port, whereby said carrier gas passes to the outlet conduitand the sample gas passes through said loop to the vent conduit, saidmovable element :in the second position connecting said `first port tosaid third port, said second port to said fifth port and said sixth portto said fourth port whereby the carrier gas passes through the loop tothe outlet conduit and said sample gas passes to the vent conduit; amotor valve in said sample line, and means operatively connecting saidmotor valve to said timing means to cause said motor valve to close apredetermined short time before said movable element moves from saidfirst position to said second position during each cycle, therebypermitting the pressure of the sample gas contained in said loop to dropto atmospheric pressure before the sample gas trapped in said loop ispassed to said outlet conduit, thereby preventing variations in thepressure and hence in the amount of the sample gas passing to saidoutlet conduit during each cycle of operation.

2. A sampling system for a vapor phase chromatographic analyzer whichcomprises, in combination, a valve having six ports formed therein andcomprising a fixed element and a movable element, a sample inlet lineconnected to the first port of said v-alve, a carrier gas inlet lineconnected to the second port of said valve, a vent conduit connected tothe third port of said valve, an outlet conduit connected to rthe fourthport of said valve, and a conduit or loop connected between the fifthand sixth ports of said valve, a chromatographic column packed withabsorptive material having one end thereof connected to said outletconduit, an eiuent conduit connected to the other end of said column,means for measuring the thermal conductivity of material passing throughsaid eflluent conduit, timing means cyclically operable to move saidmovable element to a first position during one portion of each cycle andto move said movable element to a second position during another portionof each cycle, said movable element in the first position connectingsaid first port to said fifth port,4 said sixth port to said third port,and second port to said fourth port whereby the carrier gas passes tothe outlet conduit and the sample gas passes through said loop to thevent conduit, said movable element in the second position connectingsaid first port to said third port, said second port to said fifth port,and said sixth port to said fourth port whereby the carrier gas passesthrough the loop to the outlet conduit and the sample gas passes to thevent conduit, a motor valve in said sample inlet line, means operativelyconnecting said motor valve: to said timing means to cause said motorvalve to close a predetermined short time before said movable elementmoves from said first position to said second position during eachcycle, thereby permitting the pressure of the sample gas contained insaid loop to drop to atmospheric pressure before the sample gas trappedin said loop is passed to said outlet conduit, thereby preventingvariations in the pressure and hence in the amount of the sample gaspassing to said outlet conduit during each cycle of operation.

3. A sampling system for an analytical instrument comprising a conduithaving an inlet `and an outlet, a sample line to supply a iiuid to beanalyzed, first means for connecting the outlet of said sample line tosaid inlet of said conduit and for venting said outlet of said conduitto the atmosphere during a first portion of each of a plurality ofsuccessive cycles of operation, an outlet line, second means forconnecting said outlet of said conduit to said outlet line during asecond portion of each of said plurality of successive cycles ofoperation, means for displacing during said second portion the sampletrapped in said conduit `from said conduit into said outlet line, avalve in said sample line, timing means to operate said first means andsaid second means, and

means responsive to said timing means to close said valve apredetermined short time before the end of said first portion of eachcycle, thereby permitting the pressure of the fluid contained in saidconduit to drop to atmospheric pressure before the fluid trapped ins-aid conduit is passed to said outlet line, thereby preventingvariations in the pressure of and hence in the amount of the uid passingto said outlet line during each cycle of operation.

4. A chromatographic analyzing system for analyzing a sample which canform a combustible mixture With air, comprising, a chromatographiccolumn containing absorbent material, a valve means having six ports, asample inlet line connected to a first port of said valve means, aninert carrier gas inlet line connected to a second port of said valvemeans, a vent conduit connected to a third port of said valve means, anoutlet line connected between a fourth port of said valve means and afirst end of said chromatographic column, a sample-collecting conduitconnected between fifth and sixth ports of said valve means, said valvemeans being operable in one position to connect said sample inlet linethrough said sample-collecting conduit to said vent conduit and toconnect said carrier gas inlet line to said chromatographic columnthrough said outlet line, said valve means being operable in a secondposition to connect said sample inlet line to said vent conduit and toconnect said carrier gas inlet line to said chromatographic columnthrough said sample-collecting conduit and said outlet line, a valvehousing enclosing said valve means and having an inlet and an outlet, ameasuring cell for measuring a property of the effluent from saidchromatographic column, and means for passing the efuent gas, which isessentially inert with respect to combustibility, from saidchromatographic column through said cell and through said inlet of saidvalve housing into the interior of said valve housing, whereby theessentially inert effluent gas acts as a purging medium to prevent theformation of a combustil2 ble mixture in the area of said valve meansdue to possible leakage of the sample at the ports of said valve means.

5. A sampling system for an analytical instrument for analyzing a samplewhich can form a combustible mixture with air comprising, a firstconduit means to supply an inert carrier gas, second conduit means tosupply a sample gas, third conduit means to store said sample gas, valvemeans communicating with said rst, second and third conduit means andthe inlet of said instrument so that said sample gas is passed throughsaid third conduit means when said valve means is in a first positionand said carrier gas is passed through said third conduit means to theinlet of said instrument when said valve means is in a second position,a housing enclosing said valve means, said housing having an inlet andan outlet therein, fourth conduit means communicating between the outletof said instrument and the inlet of said housing so that the efliuentgas, which is essentially inert with respect to combustibility, fromsaid instrument acts as a purging medium to prevent the formation of acombustible mixture in the area of said valve means due to possibleleakage of the sample gas at the ports of said valve means.

References Cited in the tile of this patent UNITED STATES PATENTS2,757,541 Watson et al. Aug. 7, 1956 2,830,738 Sorg et al. Apr. 15, 19582,833,151 Harvey May 6, 1958 OTHER REFERENCES Article by Lichtenfels etal. in Analytical Chemistr, vol. 28, September 1956, pages 1376-1379.(Copy in 73-23C.)

Article: Gas Chromatography in Plant Streams, D. Fuller, published inISA Journal, November 1956, pp. 440, 444. l(Copy in 73-23C.)

